US9394580B2 - High-toughness cold-drawn non-heat-treated wire rod, and method for manufacturing same - Google Patents

High-toughness cold-drawn non-heat-treated wire rod, and method for manufacturing same Download PDF

Info

Publication number
US9394580B2
US9394580B2 US13/824,667 US201113824667A US9394580B2 US 9394580 B2 US9394580 B2 US 9394580B2 US 201113824667 A US201113824667 A US 201113824667A US 9394580 B2 US9394580 B2 US 9394580B2
Authority
US
United States
Prior art keywords
wire rod
less
cold
heat treated
cooling
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active, expires
Application number
US13/824,667
Other versions
US20130174947A1 (en
Inventor
You-Hwan Lee
Dong-Hyun Kim
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Posco Holdings Inc
Original Assignee
Posco Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Posco Co Ltd filed Critical Posco Co Ltd
Assigned to POSCO reassignment POSCO ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KIM, DONG-HYUN, LEE, YOU-HWAN
Publication of US20130174947A1 publication Critical patent/US20130174947A1/en
Application granted granted Critical
Publication of US9394580B2 publication Critical patent/US9394580B2/en
Assigned to POSCO HOLDINGS INC. reassignment POSCO HOLDINGS INC. CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: POSCO
Assigned to POSCO CO., LTD reassignment POSCO CO., LTD ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: POSCO HOLDINGS INC.
Active legal-status Critical Current
Adjusted expiration legal-status Critical

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C1/00—Manufacture of metal sheets, metal wire, metal rods, metal tubes by drawing
    • B21C1/003—Drawing materials of special alloys so far as the composition of the alloy requires or permits special drawing methods or sequences
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/10—Modifying the physical properties of iron or steel by deformation by cold working of the whole cross-section, e.g. of concrete reinforcing bars
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a wire rod for use in mechanical structure connections, vehicle components, or the like, and more specifically, to a non-heat treated wire rod having excellent toughness, in which even in the case that a heating operation is omitted, strength may be secured through a cold drawing process, and a method for manufacturing the same.
  • Non-heat treated steel is a steel that does not undergo a heat treatment after hot working, but has a similar toughness and strength to a steel that has undergone a heat treatment (heat treated steel).
  • Non-heat treated steel may be also called a “micro-alloyed steel” since the quality of the material is obtained by adding a very small amount of an alloying element.
  • a typical wire rod product is produced as a final product through the operations of Hot Rolling ⁇ Cold Drawing ⁇ Spheroidization Heat treatment ⁇ Cold Drawing ⁇ Cold Forging ⁇ Quenching and Tempering, whereas a non-heat treated steel is produced through the operations of Hot Rolling ⁇ Cold Drawing ⁇ Cold Forging ⁇ Product.
  • the non-heat treated steel is an economical product that may be produced without heat treatment and at the same time, does not undergo a final quenching and tempering process. Therefore, non-heat treated steel has been applied to many products due to the securing of linearity obtained by not generating heating deflections, i.e., defects caused during heating.
  • Japanese Patent Laid-Open Publication No. 1995-054040 discloses a method for providing a non-heat treated steel wire rod with 750-950 MPa of tension by hot rolling the alloy steel that is composed of C: 0.1-0.2%, Si: 0.05-0.5%, Mn: 1.0-2.0%, Cr: 0.05-0.3%, Mo: 0.1% or less, V: 0.05-0.2%, Nb: 0.005-0.03%, and the remainder Fe, as a percentage by weight, cooling the alloy steel within 60 seconds between 800-600° C. for a cooling operation, and heating at 450-600° C., or cooling the alloyed steel after continuously maintaining it at a temperature of between 600-450° C. for at least 20 minutes, and then cold working.
  • the product is hot-rolled through a process known as controlled rolling, and relatively expensive components such as chromium (Cr), molybdenum (Mo), vanadium (V), and the like are added in the method as mentioned above, so that it is uneconomical in practical use.
  • relatively expensive components such as chromium (Cr), molybdenum (Mo), vanadium (V), and the like are added in the method as mentioned above, so that it is uneconomical in practical use.
  • Japanese Patent Laid-Open Publication No. 1998-008209 relates to non-heat treated steel with excellent strength after hot working, and excellent cold formability and a method for manufacturing the same, and a method for preparing a forging member by using a non-heat treated steel, and also relates to non-heat treated steel with excellent cold formability, in which a volume of a ferrite phase is at least 40%, and a hardness is 90 HRB or less, for the steel having a controlled contents of carbon (C), silicon (Si), manganese (Mn), Cr, V, phosphorus (P), oxygen (O), sulfur (S), tellurium (Te), lead (Pb), bismuth (Bi), and calcium (Ca).
  • the document relates to a method for continuously cooling to an Al point temperature or less at cooling rate of 120° C. or less per minute, immediately after hot-rolling at 800-950° C. during a final working temperature, a method for cooling a hot rolled steel material in the air after heating for at least 10 minutes at 800-950° C., and also, a method for preparing a structural member with 20-35 HRB of hardness by cold working or warm working at a temperature of 600° C. or less, preparing a preform, and air cooling after hot-forging the preform at 1000-1250° C.
  • the technology is limited to a specific steel containing elements that are usually not used, and is not applied to cold forging.
  • Japanese Patent Laid-Open Publication No. 2006-118014 provides a method for manufacturing case-hardened steel that is suitable for a bolt, and the like, which suppresses grain coarsening after heat treatment, even if cold formability is excellent and also, working with a high cutting rate of an expanded line is performed.
  • the method as mentioned above uses the steel material that is composed of C: 0.1-0.25%, Si: 0.5% or less, Mn: 0.3-1.0%, P: 0.03% or less, S: 0.03% or less, Cr: 0.3-1.5%, aluminum (Al): 0.02-0.1%, N: 0.005-0.02%, the remainder iron (Fe), and other inevitable impurities, as a percentage by weight, and the method for manufacturing non-heat treated wire rod with excellent toughness is achieved by performing hot finish rolling or hot finish forging at 700-850° C., then cooling by up to 600° C. at a cooling rate of 0.5° C./sec or less, and suppressing a cut rate of an expanded line to below 20% by cooling to room temperature.
  • the technology as mentioned above discloses the use of a small amount of Mn, and the use of Cr and Al.
  • An aspect of the present invention provides a high toughness cold-drawn non-heat treated wire rod that may allow for control of tensile strength through cold drawing and has excellent toughness, and a method for manufacturing the same.
  • a high toughness cold-drawn non-heat treated wire rod including carbon (C): 0.2-0.3%, silicon (Si): 0.1-0.2%, manganese (Mn): 2.5-4.0%, phosphorus (P): 0.035% or less (except 0), sulfur (S): 0.04% or less (except 0), the remainder iron (Fe), and other inevitable impurities, as a percentage by weight.
  • a method for manufacturing a high toughness cold-drawn non-heat treated wire rod including heating a billet that includes C: 0.2-0.3%, Si: 0.1-0.2%, Mn: 2.5-4.0%, P: 0.035% or less (except 0), S: 0.04% or less (except 0), the remainder Fe, and other inevitable impurities, as a percentage by weight, within a temperature range of A e3 +150° C. to A e3 +250° C.;
  • the present invention can provide a non-heat treated wire rod that can secure excellent high toughness even if a heat treatment is omitted, and in particular, can control tensile strength only through cold drawing, and can effectively manufacture parts for vehicles requiring high degrees of toughness, for example, a tie rod, a rack bar, etc. through this non-heat treated wire rod.
  • FIG. 1 shows the microstructure of Inventive Example 3 in Embodiment 2;
  • FIG. 2 shows the microstructure of Comparative Wire Rod 6 in Example 2
  • FIG. 3 is a magnified image of pearlite in the photograph of FIG. 1 ;
  • FIG. 4 is a magnified image of pearlite in the photograph of FIG. 2 ;
  • FIG. 5 is a graph showing the measurement of an increase in strength according to the level of cold drawing in Example 2.
  • FIG. 6 is a graph showing the measurement of impact toughness according to the level of cold drawing in Example 2.
  • the present inventors perceived that unlike existing techniques, a carbon diffusion suppression effect is generated by increasing the content of Mn and controlling the cooling rate during the manufacturing process, to thus form de-generated pearlite different from existing pearlite, and which is therefore capable of enhancing toughness, especially impact toughness, and they thereby completed the present invention.
  • composition of a wire rod of the present invention will be described in detail (hereinafter, weight %).
  • the composition of the wire rod of the present invention is characterized in that excellent toughness may be secured even if a high price element is not particularly added.
  • Carbon (C) content is preferably provided in a range of 0.2-0.3%.
  • C is an element having an influence on the strength of the wire rod, and is added in an amount of 0.2% or more so as to secure sufficient strength.
  • the C content is preferably limited to 0.3 wt % or less.
  • Silicon (Si) is preferably within a range 0.1-0.2%.
  • a Si content should be preferably 0.2% or less.
  • the Si content is preferably limited to not less than 0.1%.
  • Manganese (Mn) is preferably within a range of 2.5-4.0%.
  • Mn is an element for solid solution strengthening that forms substitutional solid solutions in a matrix. For this reason, Mn is a useful element that may secure a required degree of strength without any deterioration of ductility. When a Mn content exceeds 4.0%, ductility decreases sharply due to Mn segregation, rather than the effect of solid solution strengthening.
  • Phosphorus (P) and sulfur (S) are preferably present in ranges of not more than 0.035% (except 0) and of not more than 0.40% (except 0), respectively. Since P is a major cause of deteriorated toughness by segregation into grain boundaries, the upper limit of P is limited to 0.035%. Since S is a low melting point element and segregates into grain boundaries to deteriorate toughness and form sulphides, thus having a harmful influence on the properties of delayed fracture resistance and stress relaxation, the upper limit of S content is preferably limited to 0.040%.
  • the remainder includes iron (Fe) and unavoidable impurities. It is not intended that the wire rod of the present invention is entirely free of any element other than the above-mentioned elements.
  • the wire rod of the present invention includes pearlite having an area fraction of not less than 90%, and the remainder, ferrite.
  • the pearlite has de-generated pearlite including cementite having a thickness of not more than 100 nm.
  • the de-generated pearlite has an aspect ratio of not more than 30:1 (width:thickness) which is an average aspect ratio of cementite, and forms a lamella structure having a lamella ferrite form together with partially segmented cementite.
  • Mn segregates into grain boundaries between ferrite and austenite to suppress decomposition of austenite, so that non-equilibrium phase appears due to a dragg effect.
  • the thickness of cementite is known as lamellar spacing.
  • lamellar spacing is not more than 100 nm, cementite becomes non-uniform, and thus it becomes possible to form de-generated pearlite through de-generated lamellar.
  • the aspect ratio of cementite constituting the de-generated pearlite is 30:1 or less because cementite does not form uniform lamellar structures but is spheroidized to form de-generated lamellar. For this reason, when an impact is applied to the segmented cementites, impact energy does not pass through cementite but passes between the segmented cementites. Therefore, it is possible to enhance the impact value. However, when the aspect ratio exceeds 30:1, the lamellar of cementite is uniform. Therefore, it is hard to enhance the impact value.
  • a billet satisfying the composition is heated.
  • the heating of the billet is preferably performed within a temperature range of A e3 +150° C. to A e3 +250° C.
  • the heating is preferably performed for 30 minutes to 1 and a half hours.
  • austenite single phase may be maintained, austenite grain coarsening may be prevented, and a remained segregation, carbide, and inclusion can be effectively dissolved.
  • the heating temperature of the billet exceeds A e3 +250° C.
  • the austenite grain is largely coarsened, so that the wire rod with a high strength and excellent toughness may not be obtained because the final microstructure formed after cooling has a strong tendency to be coarsened.
  • a heating temperature of the billet is below A e3 +150° C., the heating effect may not be achieved.
  • the heating time When the heating time is below 30 minutes, there is a problem in that the overall temperature may not be even; when the heating time exceeds 1 and a half hours, the austenite grain is coarsened, and productivity is significantly decreased. Accordingly, it is preferable that the heating time does not exceed 1 and a half hours.
  • the heated billet is cooled at a cooling rate of 5-15° C./s and is rolled within a temperature range of A e3 +50° C. to A e3 +150° C./s.
  • the cooling rate is limited with the object of minimizing the transformation of microstructure in the cooling operation before hot rolling.
  • the cooling rate before hot rolling is below 5° C./s, the productivity thereof is reduced, and additional equipment is needed in order to maintain air-cooling.
  • the strength and toughness of the wire rod after completing hot rolling may be deteriorated.
  • the cooling rate exceeds 15° C./s, the possibility of new microstructures being formed during rolling is increased by increasing the driving force of the transformation of the billet before rolling, and serious problems in which the rolling temperature should be reset to a lower temperature may be caused. Therefore, the cooling rate is preferably set to 15° C./s or less.
  • Rolling after cooling in the temperature range of A e3 +50° C. to A e3 +100° C. suppresses the appearance of microstructures due to transformation during rolling, so that re-crystallization does not occur and only sizing rolling is possible.
  • the rolling temperature is below A e3 +50° C.
  • the intended microstructures in the present invention are difficult to acquire because the rolling temperature is close to the dynamic re-crystallization temperature, and the possibility of securing a general soft ferrite is very high.
  • the rolling temperature exceeds A e3 +100° C. there is a problem that re-heating is needed after cooling.
  • the wire rod manufactured through the rolling is preferably cooled down to 600° C. or less at a cooling rate of 0.01-0.25° C./s.
  • the cooling rate means a cooling rate that may very effectively produce de-generated pearlite and prevent C diffusion by adding Mn.
  • the cooling rate is below 0.01° C./s, since the cooling rate is too slow, the lamella or de-generated pearlite may not be produced, and cementite with a spheroidized form is produced, so that the strength thereof is sharply decreased.
  • the cooling rate exceeds 0.25° C./s, a low temperature structure is produced due to a large amount of Mn. Since the addition of Mn enhances hardenability to delay ferrite/pearlite transformation, thus producing a low temperature structure, such as martensite/bainite, it may not be expected to secure excellent cold drawability, impact toughness and ductility.
  • the wire rod of the present invention has a tensile strength ranging from 650 MPa to 750 Mpa, a cross-section reduction rate ranging from 60% to 70%, a tensile strength after manufacturing of the wire rod and cold drawing of about 95%, ranging from 1300 Mpa to 1500 Mpa, and a V-notch charpy impact toughness of 60 J or more.
  • Wire rods were manufactured with billets satisfying the compositions as described in Table 1, according to the manufacturing conditions as described in Table 2. Tensile strength and impact toughness in the manufactured wire rods were specified, and measurement results thereof are shown in Table 2.
  • Inventive Wire Rods have to have a tensile strength ranging from 650 MPa to 750 MPa. This range shows an increase in strength during cold drawing, and an optimal tensile strength range directly after hot rolling according to continuous decrease in toughness.
  • Comparative Wire Rods 1 to 3 it is not easy for Comparative Wire Rods 1 to 3 to secure a sufficient degree of strength, and it is difficult for Comparative Wire Rods 4 and 5 to secure sufficient cold drawability.
  • the cooling rate of capable of securing the most proper tensile strength and impact toughness even when the specimens are Inventive Wire Rods is in a range of 0.5-1.5° C./s. Therefore, it can be confirmed that the cooling condition can be a preferred condition. That is, Inventive Wire Rods 1-1 an 2-1 which are classified as Comparative Examples did not secure a proper degree of strength, and Inventive Wire Rods 1-5, 2-4, and 2-5 secured a proper degree of strength with insufficient impact toughness.
  • Comparative Wire Rod 6 includes 0.25 wt % of C and 0.5 wt % of Mn, and was the same in remaining condition as Inventive Wire Rod 3.
  • FIGS. 1 and 2 Microstructures of Inventive Wire Rod 3 and Comparative Wire Rod 6 were observed and are shown in FIGS. 1 and 2 , and magnified photographs thereof are shown in FIGS. 3 and 4 , respectively.
  • FIGS. 1 and 3 show microstructure of Inventive Wire Rod 3, in which black portions indicate de-generated pearlite and white portions indicate ferrite. It can be confirmed that the de-generated pearlite occupies an area fraction of not less than 90%. Also, it can be confirmed from FIG. 3 that ferrite and cementite form a mixed phase, but do not a lamellar structure, unlike typical pearlite.
  • FIGS. 2 and 4 show microstructure of Comparative Wire Rod 6, i.e., a typical ferrite-based steel sheet. It can be confirmed from FIG. 4 that ferrite occupies an area fraction of about 80%, pearlite occupies an area fraction of about 20%, and the pearlite has a lamellar structure composed of ferrites and cementites.
  • 25F, 45F, 45C and 82BC indicate 25F steel having a component of 0.25C-0.7Mn-0.2Si, 45F and 45C steels having a component of 0.45C-0.7Mn-0.2Si, and 82BC steel having a component of 0.9C-0.7Mn-0.2Cr, respectively.
  • Inventive Material 3 has an impact toughness of not less than 60 J even in a cross-section reduction rate of not less than 90%, but other billets are fractured or have very low impact toughness values.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)
  • Metal Extraction Processes (AREA)
  • Metal Rolling (AREA)
  • Ropes Or Cables (AREA)

Abstract

Provided is a wire rod for use in mechanical structure connections, vehicle components, or the like, and more particularly, to a wire rod which has superior toughness without being subjected to a heat treatment, and the strength of which is ensured through a cold-drawing process. Tot his end, provided are a high-toughness cold-drawn non-heat-treated wire rod and a method for manufacturing the same, wherein the wire rod comprises in % by weight: 0.2 to 0.3% of carbon (C), 0.1 to 0.2% of silicon (Si), 2.5 to 4.0% of manganese (Mn), 0.035% or less (but not 0%) of phosphorus (P), 0.04% or less (but not 0%) of sulfur (S), the remainder being iron (Fe) and unavoidable impurities.

Description

TECHNICAL FIELD
The present invention relates to a wire rod for use in mechanical structure connections, vehicle components, or the like, and more specifically, to a non-heat treated wire rod having excellent toughness, in which even in the case that a heating operation is omitted, strength may be secured through a cold drawing process, and a method for manufacturing the same.
BACKGROUND ART
Most structural steels used as components of mechanical structures and vehicles are quenched and tempered steels obtained by increasing strength and toughness through reheating, quenching, and tempering after hot working. On the contrary, a non-heat treated steel is a steel that does not undergo a heat treatment after hot working, but has a similar toughness and strength to a steel that has undergone a heat treatment (heat treated steel). Non-heat treated steel may be also called a “micro-alloyed steel” since the quality of the material is obtained by adding a very small amount of an alloying element.
Generally, a typical wire rod product is produced as a final product through the operations of Hot Rolling→Cold Drawing→Spheroidization Heat treatment→Cold Drawing→Cold Forging→Quenching and Tempering, whereas a non-heat treated steel is produced through the operations of Hot Rolling→Cold Drawing→Cold Forging→Product.
As described above, the non-heat treated steel is an economical product that may be produced without heat treatment and at the same time, does not undergo a final quenching and tempering process. Therefore, non-heat treated steel has been applied to many products due to the securing of linearity obtained by not generating heating deflections, i.e., defects caused during heating.
However, since the heat treatment process is omitted and cold working is continuously applied, as the processes progress, the strength of the product is further increased, while ductility is continuously decreased. To solve such drawbacks, the following techniques are disclosed.
Japanese Patent Laid-Open Publication No. 1995-054040 discloses a method for providing a non-heat treated steel wire rod with 750-950 MPa of tension by hot rolling the alloy steel that is composed of C: 0.1-0.2%, Si: 0.05-0.5%, Mn: 1.0-2.0%, Cr: 0.05-0.3%, Mo: 0.1% or less, V: 0.05-0.2%, Nb: 0.005-0.03%, and the remainder Fe, as a percentage by weight, cooling the alloy steel within 60 seconds between 800-600° C. for a cooling operation, and heating at 450-600° C., or cooling the alloyed steel after continuously maintaining it at a temperature of between 600-450° C. for at least 20 minutes, and then cold working. However, the product is hot-rolled through a process known as controlled rolling, and relatively expensive components such as chromium (Cr), molybdenum (Mo), vanadium (V), and the like are added in the method as mentioned above, so that it is uneconomical in practical use.
In addition, Japanese Patent Laid-Open Publication No. 1998-008209 relates to non-heat treated steel with excellent strength after hot working, and excellent cold formability and a method for manufacturing the same, and a method for preparing a forging member by using a non-heat treated steel, and also relates to non-heat treated steel with excellent cold formability, in which a volume of a ferrite phase is at least 40%, and a hardness is 90 HRB or less, for the steel having a controlled contents of carbon (C), silicon (Si), manganese (Mn), Cr, V, phosphorus (P), oxygen (O), sulfur (S), tellurium (Te), lead (Pb), bismuth (Bi), and calcium (Ca). Specifically, the document relates to a method for continuously cooling to an Al point temperature or less at cooling rate of 120° C. or less per minute, immediately after hot-rolling at 800-950° C. during a final working temperature, a method for cooling a hot rolled steel material in the air after heating for at least 10 minutes at 800-950° C., and also, a method for preparing a structural member with 20-35 HRB of hardness by cold working or warm working at a temperature of 600° C. or less, preparing a preform, and air cooling after hot-forging the preform at 1000-1250° C. However, the technology is limited to a specific steel containing elements that are usually not used, and is not applied to cold forging.
In addition, Japanese Patent Laid-Open Publication No. 2006-118014 provides a method for manufacturing case-hardened steel that is suitable for a bolt, and the like, which suppresses grain coarsening after heat treatment, even if cold formability is excellent and also, working with a high cutting rate of an expanded line is performed. The method as mentioned above uses the steel material that is composed of C: 0.1-0.25%, Si: 0.5% or less, Mn: 0.3-1.0%, P: 0.03% or less, S: 0.03% or less, Cr: 0.3-1.5%, aluminum (Al): 0.02-0.1%, N: 0.005-0.02%, the remainder iron (Fe), and other inevitable impurities, as a percentage by weight, and the method for manufacturing non-heat treated wire rod with excellent toughness is achieved by performing hot finish rolling or hot finish forging at 700-850° C., then cooling by up to 600° C. at a cooling rate of 0.5° C./sec or less, and suppressing a cut rate of an expanded line to below 20% by cooling to room temperature. The technology as mentioned above discloses the use of a small amount of Mn, and the use of Cr and Al.
DISCLOSURE Technical Problem
An aspect of the present invention provides a high toughness cold-drawn non-heat treated wire rod that may allow for control of tensile strength through cold drawing and has excellent toughness, and a method for manufacturing the same.
According to an aspect of the present invention, there is provided a high toughness cold-drawn non-heat treated wire rod including carbon (C): 0.2-0.3%, silicon (Si): 0.1-0.2%, manganese (Mn): 2.5-4.0%, phosphorus (P): 0.035% or less (except 0), sulfur (S): 0.04% or less (except 0), the remainder iron (Fe), and other inevitable impurities, as a percentage by weight.
According to another aspect of the present invention, there is provided a method for manufacturing a high toughness cold-drawn non-heat treated wire rod, including heating a billet that includes C: 0.2-0.3%, Si: 0.1-0.2%, Mn: 2.5-4.0%, P: 0.035% or less (except 0), S: 0.04% or less (except 0), the remainder Fe, and other inevitable impurities, as a percentage by weight, within a temperature range of Ae3+150° C. to Ae3+250° C.;
cooling the heated billet at a cooling rate of 5-15° C./s; and
rolling the cooled billet within a temperature range of Ae3+50° C. to Ae3+150° C.; and cooling the rolled steel to a temperature of 600° C. or less.
The present invention can provide a non-heat treated wire rod that can secure excellent high toughness even if a heat treatment is omitted, and in particular, can control tensile strength only through cold drawing, and can effectively manufacture parts for vehicles requiring high degrees of toughness, for example, a tie rod, a rack bar, etc. through this non-heat treated wire rod.
DESCRIPTION OF DRAWINGS
FIG. 1 shows the microstructure of Inventive Example 3 in Embodiment 2;
FIG. 2 shows the microstructure of Comparative Wire Rod 6 in Example 2;
FIG. 3 is a magnified image of pearlite in the photograph of FIG. 1;
FIG. 4 is a magnified image of pearlite in the photograph of FIG. 2;
FIG. 5 is a graph showing the measurement of an increase in strength according to the level of cold drawing in Example 2; and
FIG. 6 is a graph showing the measurement of impact toughness according to the level of cold drawing in Example 2.
 DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The present inventors perceived that unlike existing techniques, a carbon diffusion suppression effect is generated by increasing the content of Mn and controlling the cooling rate during the manufacturing process, to thus form de-generated pearlite different from existing pearlite, and which is therefore capable of enhancing toughness, especially impact toughness, and they thereby completed the present invention.
First, the composition of a wire rod of the present invention will be described in detail (hereinafter, weight %). The composition of the wire rod of the present invention is characterized in that excellent toughness may be secured even if a high price element is not particularly added.
Carbon (C) content is preferably provided in a range of 0.2-0.3%. C is an element having an influence on the strength of the wire rod, and is added in an amount of 0.2% or more so as to secure sufficient strength. However, when a C content is excessive, the tendency for a ferrite and pearlite microstructure being formed is also increased, and thus more strength than is required is secured, thereby degrading toughness. Therefore, the C content is preferably limited to 0.3 wt % or less.
Silicon (Si) is preferably within a range 0.1-0.2%. To solve deterioration of workability due to sharp increase in work-hardening during cold drawing and forging, a Si content should be preferably 0.2% or less. When the Si content is so low, there is a problem in that the strength level that is required for hot rolled steel and the final product cannot be reached. Therefore, the Si content is preferably limited to not less than 0.1%.
Manganese (Mn) is preferably within a range of 2.5-4.0%. Mn is an element for solid solution strengthening that forms substitutional solid solutions in a matrix. For this reason, Mn is a useful element that may secure a required degree of strength without any deterioration of ductility. When a Mn content exceeds 4.0%, ductility decreases sharply due to Mn segregation, rather than the effect of solid solution strengthening. That is, when the Mn content is excessive, macro segregation and micro segregation easily occur according to a segregation mechanism during the solidification of steel to form a segregation zone due to a relatively low diffusion coefficient as compared to other elements, and the formed segregation zone becomes a major cause of forming a low temperature structure (core martensite) in a core portion, so that strength increases but ductility decreases. Also, when the Mn content is less than 2.5%, there is little effect on the segregation zone due to the segregation of Mn, but it is hard to sufficiently secure de-generated pearlite which is required in the present invention, and it is also hard to secure excellent cold drawability.
Phosphorus (P) and sulfur (S) are preferably present in ranges of not more than 0.035% (except 0) and of not more than 0.40% (except 0), respectively. Since P is a major cause of deteriorated toughness by segregation into grain boundaries, the upper limit of P is limited to 0.035%. Since S is a low melting point element and segregates into grain boundaries to deteriorate toughness and form sulphides, thus having a harmful influence on the properties of delayed fracture resistance and stress relaxation, the upper limit of S content is preferably limited to 0.040%.
The remainder includes iron (Fe) and unavoidable impurities. It is not intended that the wire rod of the present invention is entirely free of any element other than the above-mentioned elements.
Hereinafter, the microstructure of the wire rod of the present invention will be described in detail.
The wire rod of the present invention includes pearlite having an area fraction of not less than 90%, and the remainder, ferrite. The pearlite has de-generated pearlite including cementite having a thickness of not more than 100 nm. The de-generated pearlite has an aspect ratio of not more than 30:1 (width:thickness) which is an average aspect ratio of cementite, and forms a lamella structure having a lamella ferrite form together with partially segmented cementite.
In the present invention, since as the Mn content increases, C activity decreases, and a non-equilibrium structure, i.e., de-generated pearlite, may be formed. Mn segregates into grain boundaries between ferrite and austenite to suppress decomposition of austenite, so that non-equilibrium phase appears due to a dragg effect.
The thickness of cementite is known as lamellar spacing. In the present invention, when lamellar spacing is not more than 100 nm, cementite becomes non-uniform, and thus it becomes possible to form de-generated pearlite through de-generated lamellar.
The aspect ratio of cementite constituting the de-generated pearlite is 30:1 or less because cementite does not form uniform lamellar structures but is spheroidized to form de-generated lamellar. For this reason, when an impact is applied to the segmented cementites, impact energy does not pass through cementite but passes between the segmented cementites. Therefore, it is possible to enhance the impact value. However, when the aspect ratio exceeds 30:1, the lamellar of cementite is uniform. Therefore, it is hard to enhance the impact value.
Hereinafter, a method for manufacturing a wire rod according to the present invention will be described in more detail.
A billet satisfying the composition is heated. The heating of the billet is preferably performed within a temperature range of Ae3+150° C. to Ae3+250° C. For example, the heating is preferably performed for 30 minutes to 1 and a half hours.
By heating the billet within the temperature range mentioned above, austenite single phase may be maintained, austenite grain coarsening may be prevented, and a remained segregation, carbide, and inclusion can be effectively dissolved. When the heating temperature of the billet exceeds Ae3+250° C., the austenite grain is largely coarsened, so that the wire rod with a high strength and excellent toughness may not be obtained because the final microstructure formed after cooling has a strong tendency to be coarsened. On the other hand, when a heating temperature of the billet is below Ae3+150° C., the heating effect may not be achieved.
When the heating time is below 30 minutes, there is a problem in that the overall temperature may not be even; when the heating time exceeds 1 and a half hours, the austenite grain is coarsened, and productivity is significantly decreased. Accordingly, it is preferable that the heating time does not exceed 1 and a half hours.
It is preferable that the heated billet is cooled at a cooling rate of 5-15° C./s and is rolled within a temperature range of Ae3+50° C. to Ae3+150° C./s.
The cooling rate is limited with the object of minimizing the transformation of microstructure in the cooling operation before hot rolling. When the cooling rate before hot rolling is below 5° C./s, the productivity thereof is reduced, and additional equipment is needed in order to maintain air-cooling. In addition, as in the case of maintaining the heating time for a long period, the strength and toughness of the wire rod after completing hot rolling may be deteriorated. On the other hand, when the cooling rate exceeds 15° C./s, the possibility of new microstructures being formed during rolling is increased by increasing the driving force of the transformation of the billet before rolling, and serious problems in which the rolling temperature should be reset to a lower temperature may be caused. Therefore, the cooling rate is preferably set to 15° C./s or less.
Rolling after cooling in the temperature range of Ae3+50° C. to Ae3+100° C. suppresses the appearance of microstructures due to transformation during rolling, so that re-crystallization does not occur and only sizing rolling is possible. When the rolling temperature is below Ae3+50° C., the intended microstructures in the present invention are difficult to acquire because the rolling temperature is close to the dynamic re-crystallization temperature, and the possibility of securing a general soft ferrite is very high. On the other hand, when the rolling temperature exceeds Ae3+100° C., there is a problem that re-heating is needed after cooling.
The wire rod manufactured through the rolling is preferably cooled down to 600° C. or less at a cooling rate of 0.01-0.25° C./s. The cooling rate means a cooling rate that may very effectively produce de-generated pearlite and prevent C diffusion by adding Mn. When the cooling rate is below 0.01° C./s, since the cooling rate is too slow, the lamella or de-generated pearlite may not be produced, and cementite with a spheroidized form is produced, so that the strength thereof is sharply decreased. On the other hand, when the cooling rate exceeds 0.25° C./s, a low temperature structure is produced due to a large amount of Mn. Since the addition of Mn enhances hardenability to delay ferrite/pearlite transformation, thus producing a low temperature structure, such as martensite/bainite, it may not be expected to secure excellent cold drawability, impact toughness and ductility.
The wire rod of the present invention has a tensile strength ranging from 650 MPa to 750 Mpa, a cross-section reduction rate ranging from 60% to 70%, a tensile strength after manufacturing of the wire rod and cold drawing of about 95%, ranging from 1300 Mpa to 1500 Mpa, and a V-notch charpy impact toughness of 60 J or more.
Best Mode for Carrying Out the Invention
Hereinafter, the present invention will be described in detail with reference to the following Examples. The present invention is, however, not limited by the following Examples.
Example 1
Wire rods were manufactured with billets satisfying the compositions as described in Table 1, according to the manufacturing conditions as described in Table 2. Tensile strength and impact toughness in the manufactured wire rods were specified, and measurement results thereof are shown in Table 2.
TABLE 1
C Si Mn Ae3
Item (wt %) (wt %) (wt %) P (wt %) S (wt %) (° C.)
Inventive 0.20 0.10 2.5 0.035 0.040 842
Wire Rod 1
Inventive 0.20 0.15 2.9 0.031 0.031 838
Wire Rod 2
Inventive 0.25 0.14 3.5 0.021 0.022 836
Wire Rod 3
Inventive 0.30 0.20 4.0 0.027 0.039 835
Wire Rod 4
Comparative 0.14 0.11 1.9 0.031 0.023 863
Wire Rod 1
Comparative 0.22 0.05 1.8 0.030 0.032 855
Wire Rod 2
Comparative 0.21 0.10 1.5 0.031 0.039 851
Wire Rod 3
Comparative 0.34 0.20 3.4 0.029 0.034 833
Wire Rod 4
Comparative 0.35 0.19 2.6 0.029 0.028 829
Wire Rod 5
TABLE 2
Heating
temp.
and
time Cooling Rolling Cooling
of rate temp. rate
billet of of after Tensile V-impact
(° C., billet billet rolling strength toughness
Item min) (° C./s) (° C.) (° C./s) (MPa) (J)
Inventive 1082, 9.7 989 0.01 652 256
Wire Rod 1 80
Inventive 1038, 10.2 972 0.09 663 248
Wire Rod 2 79
Inventive 1036, 10.6 976 0.16 678 252
Wire Rod 3 88
Inventive 1035, 9.5 962 0.25 702 234
Wire Rod 4 71
Comparative 1063, 7.5 1055 0.005 520 340
Wire Rod 1 82
Comparative 1055, 8 998 0.005 558 352
Wire Rod 2 89
Comparative 1051, 9.3 965 0.008 589 312
Wire Rod 3 75
Comparative 1033, 12.1 980 1.0 892 46
Wire Rod 4 69
Comparative 1029, 11.5 968 0.9 920 13
Wire Rod 5 68
As seen from the results of Table 2, Inventive Wire Rods have to have a tensile strength ranging from 650 MPa to 750 MPa. This range shows an increase in strength during cold drawing, and an optimal tensile strength range directly after hot rolling according to continuous decrease in toughness.
Therefore, it is not easy for Comparative Wire Rods 1 to 3 to secure a sufficient degree of strength, and it is difficult for Comparative Wire Rods 4 and 5 to secure sufficient cold drawability.
Example 2
Meanwhile, preferred tensile strength and impact characteristic were observed while varying the cooling rate after hot rolling. For this purpose, billets for Inventive Wire Rods 1 and 2 were applied to the process of Table 3 to specify tensile strength and impact toughness, and measurement results thereof are shown in Table 3. More preferred cooling rate condition may be confirmed through the results of Table 3.
TABLE 3
Heating
temp.
and Cooling Rolling Cooling
time of rate temp. rate
billet of of after Tensile V-impact
(° C., billet billet rolling strength toughness
Item min) (° C./s) (° C.) (° C./s) (MPa) (J) Note
Inventive 1082, 9.7 989 1.3 652 256 Inventive
Wire
80 Example
Rod 1
Inventive 1090, 13.2 956 0.2 531 326 Inventive
Wire 62 Example
Rod 1-1
Inventive 1015, 11.9 978 0.5 653 261 Inventive
Wire 71 Example
Rod 1-2
Inventive 1065, 10.2 988 0.9 676 235 Inventive
Wire 65 Example
Rod 1-3
Inventive 1111, 9.6 990 1.5 681 221 Inventive
Wire 88 Example
Rod 1-4
Inventive 1093, 13.9 991 2.3 897 32 Inventive
Wire 78 Example
Rod 1-5
Inventive 1038, 10.2 972 0.8 663 248 Inventive
Wire 79 Example
Rod 2
Inventive 1082, 11.7 965 0.3 546 365 Inventive
Wire 82 Example
Rod 2-1
Inventive 1053, 12.4 978 0.6 659 223 Inventive
Wire 82 Example
Rod 2-2
Inventive 1065, 10.2 981 1.1 675 232 Inventive
Wire 89 Example
Rod 2-3
Inventive 1071, 9.1 980 1.7 873 41 Comparative
Wire 79 Example
Rod 2-4
Inventive 1069, 14.2 968 1.9 901 15 Comparative
Wire
80 Example
Rod 2-5
As shown in Table 3, it can be seen that the cooling rate of capable of securing the most proper tensile strength and impact toughness even when the specimens are Inventive Wire Rods is in a range of 0.5-1.5° C./s. Therefore, it can be confirmed that the cooling condition can be a preferred condition. That is, Inventive Wire Rods 1-1 an 2-1 which are classified as Comparative Examples did not secure a proper degree of strength, and Inventive Wire Rods 1-5, 2-4, and 2-5 secured a proper degree of strength with insufficient impact toughness.
Example 3
To confirm an effect on strength increase and an effect on impact toughness, Inventive Wire Rod 3 (according to the condition of Tables 1 and 2) and Comparative Wire Rod 6 of Example 1 were prepared.
Comparative Wire Rod 6 includes 0.25 wt % of C and 0.5 wt % of Mn, and was the same in remaining condition as Inventive Wire Rod 3.
Microstructures of Inventive Wire Rod 3 and Comparative Wire Rod 6 were observed and are shown in FIGS. 1 and 2, and magnified photographs thereof are shown in FIGS. 3 and 4, respectively.
FIGS. 1 and 3 show microstructure of Inventive Wire Rod 3, in which black portions indicate de-generated pearlite and white portions indicate ferrite. It can be confirmed that the de-generated pearlite occupies an area fraction of not less than 90%. Also, it can be confirmed from FIG. 3 that ferrite and cementite form a mixed phase, but do not a lamellar structure, unlike typical pearlite.
On the contrary, FIGS. 2 and 4 show microstructure of Comparative Wire Rod 6, i.e., a typical ferrite-based steel sheet. It can be confirmed from FIG. 4 that ferrite occupies an area fraction of about 80%, pearlite occupies an area fraction of about 20%, and the pearlite has a lamellar structure composed of ferrites and cementites.
Meanwhile, strength increase and impact toughness according to cold drawing were observed and shown in FIGS. 5 and 6, respectively. In FIGS. 5 and 6, 25F, 45F, 45C and 82BC indicate 25F steel having a component of 0.25C-0.7Mn-0.2Si, 45F and 45C steels having a component of 0.45C-0.7Mn-0.2Si, and 82BC steel having a component of 0.9C-0.7Mn-0.2Cr, respectively.
As shown in FIG. 5, it can be confirmed that steels other than Inventive Material 3 and 82BC steel increase in tensile strength together with an increase in level of cold drawing and are fractured on the way. Meanwhile, as shown in FIG. 6, while the level of cold drawing increases, Inventive Material 3 has an impact toughness of not less than 60 J even in a cross-section reduction rate of not less than 90%, but other billets are fractured or have very low impact toughness values.
Accordingly, it can be confirmed that only Inventive Material 3 secures excellent strength and at the same time has an excellent impact toughness value while the level of cold drawing is increased.

Claims (7)

The invention claimed is:
1. A high toughness cold-drawn non-heat treated wire rod comprising carbon (C): 0.2-0.3%, silicon (Si): 0.1-0.2%, manganese (Mn): 2.5-4.0%, phosphorus (P): 0.035% or less (except 0), sulfur (S): 0.04% or less (except 0), the remainder iron (Fe), and other inevitable impurities, as a percentage by weight, wherein the microstructure of the wire rod is de-generated pearlite having an area fraction of not less than 90%, and ferrite.
2. The high toughness cold-drawn non-heat treated wire rod of claim 1, wherein the de-generated pearlite comprises cementite having a thickness of not more than 100 nm.
3. The high toughness cold-drawn non-heat treated wire rod of claim 1, wherein the de-generated pearlite comprises cementite having an aspect ratio (width:thickness) of 30:1 or less.
4. The high toughness cold-drawn non-heat treated wire rod of claim 1, wherein the wire rod has a tensile strength ranging from 650 Mpa to 750 Mpa.
5. The high toughness cold-drawn non-heat treated wire rod of claim 1, wherein the wire rod has a tensile strength ranging from 1300 Mpa to 1500 Mpa and a V-impact toughness of 60 J or more after cold drawing at a cross-section reduction rate of 90%.
6. A method for manufacturing a high toughness cold-drawn non-heat treated wire rod, comprising:
heating a billet that includes C: 0.2-0.3%, Si: 0.1-0.2%, Mn: 2.5-4.0%, P: 0.035% or less (except 0), S: 0.04% or less (except 0), the remainder Fe, and other inevitable impurities, as a percentage by weight, within a temperature range of Ae3+150° C. to Ae3+250° C.;
cooling the heated billet at a cooling rate of 5-15° C./s;
rolling the cooled billet within a temperature range of Ae3+50° C. to Ae3+150° C.; and
cooling the rolled steel to a temperature of 600° C. or less, wherein, after cooling, the rolled steel has a microstructure of de-generated pearlite having an area fraction of not less than 90% and, ferrite.
7. The method of claim 6, wherein the heating is performed for 30 minutes to 1 and a half hours.
US13/824,667 2010-11-19 2011-11-21 High-toughness cold-drawn non-heat-treated wire rod, and method for manufacturing same Active 2033-08-12 US9394580B2 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
KR10-2010-0115754 2010-11-19
KR1020100115754A KR101262462B1 (en) 2010-11-19 2010-11-19 Non heat treatment cold drawn wire rod having excellent impact property and method for manufacturing the same
PCT/KR2011/008883 WO2012067473A2 (en) 2010-11-19 2011-11-21 High-toughness cold-drawn non-heat-treated wire rod, and method for manufacturing same

Publications (2)

Publication Number Publication Date
US20130174947A1 US20130174947A1 (en) 2013-07-11
US9394580B2 true US9394580B2 (en) 2016-07-19

Family

ID=46084555

Family Applications (1)

Application Number Title Priority Date Filing Date
US13/824,667 Active 2033-08-12 US9394580B2 (en) 2010-11-19 2011-11-21 High-toughness cold-drawn non-heat-treated wire rod, and method for manufacturing same

Country Status (6)

Country Link
US (1) US9394580B2 (en)
EP (1) EP2641989B1 (en)
JP (1) JP5690949B2 (en)
KR (1) KR101262462B1 (en)
CN (1) CN103210106B (en)
WO (1) WO2012067473A2 (en)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101449511B1 (en) 2014-07-29 2014-10-13 한국기계연구원 Work hardenable yield ratio control steel and method for manufacturing the same
CN105648318A (en) * 2016-02-25 2016-06-08 邢台钢铁有限责任公司 Refined wire with high low-temperature high-speed torsional property and production method and application thereof
CN105734415A (en) * 2016-02-26 2016-07-06 邢台钢铁有限责任公司 Refined wire with high torsion performance and preparation method and purpose thereof
KR102047403B1 (en) * 2017-12-26 2019-11-22 주식회사 포스코 Steel wire rod for cold forging, processed good using the same, and methods for manufacturing thereof

Citations (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4578124A (en) * 1984-01-20 1986-03-25 Kabushiki Kaisha Kobe Seiko Sho High strength low carbon steels, steel articles thereof and method for manufacturing the steels
JPH01139719A (en) 1987-11-27 1989-06-01 Kawasaki Steel Corp Manufacture of high-tensile wire rod
JPH02305937A (en) 1989-05-19 1990-12-19 Sumitomo Metal Ind Ltd Fine-pearlite steel
US5141570A (en) * 1985-08-29 1992-08-25 Kabushiki Kaisha Kobe Seiko Sho High strength low carbon steel wire rods
JPH0754040A (en) 1993-08-18 1995-02-28 Daido Steel Co Ltd Manufacture of non-heat treated steel wire rod
JPH083640A (en) 1994-06-21 1996-01-09 Nippon Steel Corp Production of high-tensile non-heat treated bolt
JPH108209A (en) 1996-06-14 1998-01-13 Daido Steel Co Ltd Non-heat treated steel excellent in cold workability, its production, and production of non-heat treated steel forged member
JPH1112689A (en) 1997-06-24 1999-01-19 Kobe Steel Ltd Steel for non-heattreated bolt
CN1251865A (en) 1998-10-16 2000-05-03 浦项综合制铁株式会社 Wire materials with high drawable property and manufacture thereof
JP2000129393A (en) 1998-10-28 2000-05-09 Sumitomo Metal Ind Ltd Martensitic/bainitic non-heat treated steel excellent in machinability, and its manufacture
JP2001200332A (en) 2000-01-21 2001-07-24 Sanyo Special Steel Co Ltd High toughness non-heattreated steel
JP2001234242A (en) 2000-02-22 2001-08-28 Nippon Steel Corp Method for producing high toughness and high tensile strength steel fine in crystal grain
US6475306B1 (en) 2001-04-10 2002-11-05 Nippon Steel Corporation Hot rolled steel wire rod or bar for machine structural use and method for producing the same
JP2005133152A (en) 2003-10-30 2005-05-26 Kobe Steel Ltd High-strength wire rod to be induction-hardened superior in cold workability and impact resistance, and steel component using the wire rod
JP2006118014A (en) 2004-10-22 2006-05-11 Kobe Steel Ltd Method for producing case hardening steel having excellent cold workability and crystal grain coarsening resistance
JP2006152406A (en) 2004-11-30 2006-06-15 Kobe Steel Ltd Steel wire or bar for cold forging and production method thereof
KR100833079B1 (en) 2006-12-22 2008-05-27 주식회사 포스코 Method for manufacturing soft wire material having excellent cold forging characteristics
JP2008163410A (en) 2006-12-28 2008-07-17 Kobe Steel Ltd Steel for high-speed cold working and method for production thereof, and method for producing part formed by high-speed cold working
KR20090057564A (en) 2007-12-03 2009-06-08 주식회사 포스코 A wire rod free from heat treament having high toughness for cold forging and method for manufacturing the same
KR20090069872A (en) 2007-12-26 2009-07-01 주식회사 포스코 Steel for a structure having excellent low temperature toughnetss and tensile strength of heat affected zone and manufacturing method for the same
KR20100116991A (en) 2009-04-23 2010-11-02 주식회사 포스코 Steel wire rod having high strength and excellent toughness
WO2011016676A2 (en) * 2009-08-04 2011-02-10 Posco Non-heat treated rolled steel and drawn wire rod with excellent toughness, and method for manufacturing the same

Patent Citations (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4578124A (en) * 1984-01-20 1986-03-25 Kabushiki Kaisha Kobe Seiko Sho High strength low carbon steels, steel articles thereof and method for manufacturing the steels
US5141570A (en) * 1985-08-29 1992-08-25 Kabushiki Kaisha Kobe Seiko Sho High strength low carbon steel wire rods
JPH01139719A (en) 1987-11-27 1989-06-01 Kawasaki Steel Corp Manufacture of high-tensile wire rod
JPH02305937A (en) 1989-05-19 1990-12-19 Sumitomo Metal Ind Ltd Fine-pearlite steel
JPH0754040A (en) 1993-08-18 1995-02-28 Daido Steel Co Ltd Manufacture of non-heat treated steel wire rod
JPH083640A (en) 1994-06-21 1996-01-09 Nippon Steel Corp Production of high-tensile non-heat treated bolt
JPH108209A (en) 1996-06-14 1998-01-13 Daido Steel Co Ltd Non-heat treated steel excellent in cold workability, its production, and production of non-heat treated steel forged member
JPH1112689A (en) 1997-06-24 1999-01-19 Kobe Steel Ltd Steel for non-heattreated bolt
CN1251865A (en) 1998-10-16 2000-05-03 浦项综合制铁株式会社 Wire materials with high drawable property and manufacture thereof
US6264759B1 (en) 1998-10-16 2001-07-24 Pohang Iron & Steel Co., Ltd. Wire rods with superior drawability and manufacturing method therefor
JP2000129393A (en) 1998-10-28 2000-05-09 Sumitomo Metal Ind Ltd Martensitic/bainitic non-heat treated steel excellent in machinability, and its manufacture
JP2001200332A (en) 2000-01-21 2001-07-24 Sanyo Special Steel Co Ltd High toughness non-heattreated steel
JP2001234242A (en) 2000-02-22 2001-08-28 Nippon Steel Corp Method for producing high toughness and high tensile strength steel fine in crystal grain
US6475306B1 (en) 2001-04-10 2002-11-05 Nippon Steel Corporation Hot rolled steel wire rod or bar for machine structural use and method for producing the same
JP2005133152A (en) 2003-10-30 2005-05-26 Kobe Steel Ltd High-strength wire rod to be induction-hardened superior in cold workability and impact resistance, and steel component using the wire rod
JP2006118014A (en) 2004-10-22 2006-05-11 Kobe Steel Ltd Method for producing case hardening steel having excellent cold workability and crystal grain coarsening resistance
JP2006152406A (en) 2004-11-30 2006-06-15 Kobe Steel Ltd Steel wire or bar for cold forging and production method thereof
KR100833079B1 (en) 2006-12-22 2008-05-27 주식회사 포스코 Method for manufacturing soft wire material having excellent cold forging characteristics
JP2008163410A (en) 2006-12-28 2008-07-17 Kobe Steel Ltd Steel for high-speed cold working and method for production thereof, and method for producing part formed by high-speed cold working
KR20090057564A (en) 2007-12-03 2009-06-08 주식회사 포스코 A wire rod free from heat treament having high toughness for cold forging and method for manufacturing the same
KR20090069872A (en) 2007-12-26 2009-07-01 주식회사 포스코 Steel for a structure having excellent low temperature toughnetss and tensile strength of heat affected zone and manufacturing method for the same
KR20100116991A (en) 2009-04-23 2010-11-02 주식회사 포스코 Steel wire rod having high strength and excellent toughness
US20120037283A1 (en) * 2009-04-23 2012-02-16 Posco High-Strength, High-Toughness Steel Wire Rod, and Method for Manufacturing Same
WO2011016676A2 (en) * 2009-08-04 2011-02-10 Posco Non-heat treated rolled steel and drawn wire rod with excellent toughness, and method for manufacturing the same
US20120118443A1 (en) * 2009-08-04 2012-05-17 Posco Non-heat treated rolled steel and drawn wire rod with excellent toughness, and method for manufacturing the same

Also Published As

Publication number Publication date
EP2641989A4 (en) 2014-11-19
CN103210106B (en) 2015-07-01
WO2012067473A2 (en) 2012-05-24
JP2014503684A (en) 2014-02-13
EP2641989A2 (en) 2013-09-25
KR101262462B1 (en) 2013-05-08
KR20120054398A (en) 2012-05-30
JP5690949B2 (en) 2015-03-25
WO2012067473A3 (en) 2012-09-20
US20130174947A1 (en) 2013-07-11
EP2641989B1 (en) 2016-09-21
CN103210106A (en) 2013-07-17

Similar Documents

Publication Publication Date Title
US8715429B2 (en) Non-heat treated rolled steel and drawn wire rod with excellent toughness, and method for manufacturing the same
US6547890B2 (en) Steel wire rod for cold forging and method for producing the same
KR100517674B1 (en) Hot rolled wire or steel bar for machine structural use capable of dispensing with annealing, and method for producing the same
US6551419B2 (en) Hot-rolled steel wire and rod for machine structural use and a method for producing the same
US6673171B2 (en) Medium carbon steel sheet and strip having enhanced uniform elongation and method for production thereof
JP5492393B2 (en) Hot rolled steel bar wire and its manufacturing method
KR102065264B1 (en) Wire rod for chq capable of reducing softening treatment time, and method for manufaturing the same
JP2010144226A (en) Rolled steel material to be induction-hardened and method for manufacturing the same
KR101074297B1 (en) Process for producing steel material
US9394580B2 (en) High-toughness cold-drawn non-heat-treated wire rod, and method for manufacturing same
JP4057930B2 (en) Machine structural steel excellent in cold workability and method for producing the same
US20220033920A1 (en) Wire rod of which softening heat treatment can be omitted, and manufacturing method therefor
JP5459064B2 (en) Rolled steel for induction hardening and method for producing the same
US6475306B1 (en) Hot rolled steel wire rod or bar for machine structural use and method for producing the same
JPH0432514A (en) Production of soft wire rod free from surface abnormal phase in as-rolled state
JP5206056B2 (en) Manufacturing method of non-tempered steel
KR101318383B1 (en) Hot rolled steel sheet and methdo for manufacturing the same
JP3554506B2 (en) Manufacturing method of hot-rolled wire and bar for machine structure
JPH08199310A (en) Production of high strength martensitic stainless steel member
JP2011084784A (en) Steel to be worm-worked
KR100398388B1 (en) Manufacturing method of shaft wire with excellent impact characteristics
JPH04228519A (en) Manufacture of bar steel execellent in cold workability
KR101298699B1 (en) High strength steel and method for manufacturing the same
JPS6411083B2 (en)

Legal Events

Date Code Title Description
AS Assignment

Owner name: POSCO, KOREA, REPUBLIC OF

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:LEE, YOU-HWAN;KIM, DONG-HYUN;REEL/FRAME:030032/0660

Effective date: 20130228

STCF Information on status: patent grant

Free format text: PATENTED CASE

CC Certificate of correction
FEPP Fee payment procedure

Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 4TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1551); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 4

AS Assignment

Owner name: POSCO HOLDINGS INC., KOREA, REPUBLIC OF

Free format text: CHANGE OF NAME;ASSIGNOR:POSCO;REEL/FRAME:061561/0831

Effective date: 20220302

AS Assignment

Owner name: POSCO CO., LTD, KOREA, REPUBLIC OF

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:POSCO HOLDINGS INC.;REEL/FRAME:061777/0943

Effective date: 20221019

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 8TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1552); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 8